Caldera Chronicles: Southwest could host next U.S. volcanic eruption

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Southwest volcanoes

The San Francisco Volcanic Field is an area of young volcanoes in Northern Arizona’s Colorado Plateau that covers 1,800 square miles.

Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from Wendy Stovall, volcanologist with the U.S. Geological Survey and deputy scientist-in-charge of the Yellowstone Volcano Observatory.

There is no shortage of spectacular volcanic footage available these days. In the past few weeks we’ve seen a fissure eruption of Geldingadalur volcano in Iceland grow into spatter cones surrounded by a lava flow field, 5,000 foot-high lava fountains from Sicily’s Mount Etna, and ash plumes rocketing up to greater than 13,000 feet above Pacaya volcano in Guatemala. All of these represent possible events that could occur during the next eruption from a volcanic field in the Southwest United States.

There are thousands of volcanic features distributed throughout the Southwest, which are grouped together in volcanic fields. The U.S. Geological Survey arm of the Yellowstone Volcano Observatory is responsible for monitoring and reporting any potential hazards associated with resurgence of volcanic activity in this region. Over the past hundred or so years of volcanic research in the contiguous U.S. there has been a larger focus on the stratovolcanoes of the Cascade Range and massive calderas of Yellowstone and Long Valley than the cinder cones and lava flows of the Southwest.

This is due, in large part, to the greater hazard these large volcanoes pose to nearby population centers. This means we know relatively little about eruption timing for the majority of U.S. volcanic fields. Even so, the sparse geologic evidence we do know suggests one cinder-cone and lava-flow type eruption every 700 years in a typical volcanic field, meaning that it is more likely there will be an eruption from one of these fields during the next decades than an eruption from most Cascade volcanoes (with the exception of Mount St. Helens — the most active volcano in the Cascade Range by far).

So, what might such an eruption look like? The recent newsworthy eruptions are excellent analogs for scenarios that can occur during the next eruption in the Southwest United States.

In Iceland, red-orange lava is roiling forth from a double-vented spatter cone that feeds a surrounding lava-flow field. Volcanic gases are degrading air quality at and downwind from the eruption site. Fortunately, activity is confined to a low-lying area, which is keeping the flows from advancing very far from the eruption source.

Pacaya volcano in Guatemala has been rocketing blebs of lava into the air and sending lava flows down the volcano’s flanks for several years. Last week, an increase in eruption explosivity sent volcanic ash plumes to an altitude of 13,000 feet. Ash clouds drifted toward the airport in Guatemala city, and ashfall coated the runways and parked airplanes. Because volcanic ash is highly corrosive and can foul jet engines, government officials closed the airport.

On the island of Sicily in Italy, Etna has been putting on spectacular displays of fountaining lava that feed lava flows down the flank. Occasional explosive “paroxysms” send ash clouds into the atmosphere above the volcano. In late February, lava fountains reached a near record height of about 5,000 feet above the volcano. Earlier this month, a column of ash reached 33,000 feet, and fallout material caused “considerable inconvenience to the population of a large inhabited area.”

All of these volcanoes are erupting magma with a composition (basalt to basaltic-andesite) that is similar to the most common type for Southwest volcanoes. Unlike larger volcanoes with long-lived magma storage chambers, magma feeding cinder cones rises quickly from the mantle and is not typically stored for very long in the Earth’s crust. Most often, no obvious “volcano” exists prior to eruption (as in Iceland) — magma rises through the crust along a path of least resistance and breaks through to the surface along a fracture.

Because of this, geophysical instruments are our best tool to detect the lead up eruptions in dispersed volcanic fields. Seismometers detect rocks fracturing as magma moves, and GPS receivers and satellite imagery provide microscopic measurements of how and where the ground surface deforms in response to magma migration.

Eruptions in volcanic fields, like those of the Southwest, can last for days to years. The 1943 eruption of Paricutin, in Mexico, which lasted for nine years, is a good example of what could occur in the United States. Such an eruption today could directly impact nearby communities, air traffic, water reservoirs, transportation corridors and communications systems.

Early stages of activity would probably be similar to what we’ve seen recently in Iceland — low fountains or cauldron-like vents feeding lava flows that reach hundreds to thousands of meters away from their source. Ground topography and duration of eruption dictates how far flows will travel, but anything in their path is overrun or burned (including highways, power lines, railroads, buildings, waterways, etc.).

As eruptions progress, lava fountains could grow to hundreds of meters high and loft fine ash into the air — similar to what has occurred at Etna and Pacaya for the past month. Occasional explosions of finer ash could send plumes to altitudes used by commercial aircraft, which would close airspace and impact U.S. air traffic. Ashfall can be cleaned up, but even small amounts can damage wastewater systems, air conditioning and heating systems, and agriculture and livestock. These eruptions emit tonnes of sulfur dioxide and would degrade downwind air quality.

There are many places to view the volcanic past of the American Southwest, and to contemplate the region’s volcanic future, for example:

• The McCarty’s Flow in the Zuni-Bandera volcanic field in west-central New Mexico as part of the El Malpais National Monument.

• Sunset Crater Volcano National Monument in Arizona is located within the active San Francisco Volcanic Field.

• Uinkaret Volcanic Field is north of the western portion of the Grand Canyon, where lava flows poured into and repeatedly dammed the Colorado River.

The recent eruptions in Iceland, Italy, and Guatemala have put on spectacular displays of volcanic power. Evidence for similar activity is preserved across the American Southwest. And what happened once will certainly happen again.